The present invention relates to an improvement on a printer system wherein at least one host computer connected to a printer supplies data to the printer to print out corresponding image data, and more particularly to an improvement on a method of operating a printer system wherein a plurality of host computers use in common a single high quality printer such as a laser printer to print out according to data supplied from the computers.
In known printer systems such as photoprinters used for electronic publishings or desktop publishings such as word processors, several proposals have been hitherto made to effectively utilize memories for storing print data or like (e.g., U.S. patent application Ser. No. 145312 entitled "Method of controlling photo printer and apparatus therefor", filed on Jan. 19, 1988, by Takagishi et al and assigned to Hitachi Ltd.; or U.S. patent application Ser. No. 225782 entitled "Photo printer having a host computer support and method of controlling the same", filed on Jul. 29, 1988, by Kawamata et al and assigned to Hitachi Ltd., both being still pending) a printer is connected via data communication means to a host computer which supplies data, such as graphs, figures, photographs, characters and the like to the printer. Character pattern data for characters to be printed are stored beforehand in a memory of the host computer as well as in a memory of a printer controller of the printer. Character pattern data corresponding to inputted data is read out from the memories and converted into corresponding character image data to be printed out by a printer engine of the printer. One of such conventional system arrangements adopts a character data transfer method (Japanese Patent Laid-open Publication JP-A-61-134791). According to the method, the memory of the host computer stores therein main character pattern data, whereas the memory of the printer controller stores therein supplementary character pattern data. Character pattern data not stored in the memory of the printer controller is accessed by the host computer and transferred from the host computer to the printer controller. The character pattern data stored in the memory of the host computer is used as print data and also as display data on a CRT of the host computer for monitoring and controlling the printing.
The resolution of the image at the printer output side is required to be high so as to obtain a high print quality. In view of this, the resolution at the printer output side is set, e.g, at 48.times.48 dots in spite of the resolution of 24.times.24 dots of the CRT screen of the host computer. Therefore, with such a conventional method by which character pattern data stored at the host computer is transferred to the printer controller, the data amount to be transferred becomes large, posing a problem of long transfer time.
Apart from the above, various character types and sizes are used for applications, such as electronic publishing or desktop publishings and the like, so that the capacity of a memory storing such voluminous character pattern data becomes large. In the case where a single printer (printer controller) is used with a plurality of host computers connected thereto, every host computer has the same character pattern data in duplicate, thus posing a problem of a large memory capacity of the overall system.